The regional climate effects of large-scale agricultural irrigation related to South-to-North Water Transfer Engineering in China

Based on the agricultural geophysical classification and the land use and land cover (LULC) type map, the satellite data of multi-time, multi-spatial and multi-spectrum was used to identify the irrigation areas and their geographical locations of crops, plantations and pasture when the up-coming South-to-North Water Transfer Engineering (SNWTE) is completed by 2030. The thermal-dynamics of the soil in the irrigated area was figured out depending not only on the satellite data deduction, but also on the on-site field measurements, the data of the nearby agro-meteorologiclal and/or hydrological stations, which was used to calculate the variation regularity of soil moisture, soil temperature, albedo etc during each irrigation procedure. With reference of the methodology of pseudo-hydrodynamics in agro-hydrology, a new model module was designed to calculate the exchange and transfer process of water and heat energy in the soil-plant-atmosphere continuum (SPAC) under the condition of irrigation, which was coupled with the regional climate model RegCM3 and make it to include the irrigation effect. The new climate model was then used to simulate the will-be regional climate change in north China as if SNWTE is completed. The preliminary simulation results show that: The large-scale agriculture irrigation might cause significant regional climate change not only in Northern China where the irrigation is implemented, but in the whole numerical domain as well. During the most possible irrigation time of summer months from June to August, the ground temperature, sensible heat flux in the boundary layer decreased within irrigated region and the adjacent areas; while the low-level air humidity, latent heat flux, and precipitation are all increased. Large-scale agricultural irrigation not only changes the water vapor factors such as soil moisture and air humidity, but also the thermal factors such as temperature and sensible heat flux and the dynamic factors of potential height and wind field in the atmosphere, which cause regional climate change in the whole numerical domain.